| After a long period of evolution and development,nature has created a number of materials with special structure and excellent performance,attracting a large number of scholars at home and abroad to explore.By gaining insight into the nature of these creatures created by nature,we can provide a way to imitate nature and create new materials and structures.As an increasing popular nanofabrication technique,electrospinning has emerged as a versatile and effective method for manufacturing long continuous nanofibers.Because of its wide range of raw material sources and strong adjustability of fiber structure,electrospinning provides a basic guarantee for the research of nano bionic structure.In this paper,we reviewed various biomimetic nanofibers prepared by ellectrospinning and the application of biomimetic nanofibers in various fields.Based on the principle of electrospinning,polyvinylidene fluoride(PVDF)multi-scaled tree-like nanofibers were prepared by regulating the polymer solution properties and process parameters.A possible mechanism for the formation of the tree-like nanofibers was proposed by analyzing high speed camera photos of the spin jet,which laid the foundation for the controllable preparation of tree-like nanofibers.The tree-like structure significantly decreased the pore size and dramatically enhanced the specific surface area.Based on this,the tree-like nanofiber membrane was applied to air filtration and liquid filtration to explore the relationship between the tree-like structure and the filtration performance.PVDF tree-like nanofiber membrane loading manganese oxides(MnO2)(MnO2@PVDF tree-like nanofiber membrane)was designed by in situ polymerization of pyrrole monomer,and subsequently reacted with KMnO4 solution to deposit MnO2.and the adsorption properties of the obtained adsorbents to Pb2+ were investigated.A smart PVDF-graft-poly(acrylic acid)(PVDF-g-PAA)tree-like nanofiber membrane with pH-responsivity was fabricated through homogeneous solution polymerization and electrospinning process.The smart oil/water separation performance of the membrane under different pH was studied.The main contents of this thesis are presented as following.A novel PVDF tree-like nanofiber was fabricated via one-step electrospinning by adding certain amount of tetrabutylammonium chloride(TBAC)into PVDF solution.The effects of salt type,salt content,polymer solution concentration and process parameters on the morphology of PVDF tree-like nanofibers were studied.The results showed that the nanofibers prepared from PVDF/organic salts exhibited more tree-like structures than the nanofibers from PVDF/inorganic salts.The PVDF/TBAC(0.1 M)nanofibers formed with a voltage of 25 kV.tip to collector distance of 15 cm and spinning rate of 1 mL h-1 possessed the optimal tree-like morphology and the nanofibers were composed of trunk fibers with 100 nm-500 nm diameter and branch fibers with 5 nm-100 nm diameter.A possible mechanism for the formation of tree-like nanofibers was proposed by analyzing high speed camera photos of the spin jet and the results showed that the formation of tree-like nanofibers was due to the splitting of jets.Based on the controllable preparation of tree-like nanofiber membranes,the effects of tree-like structure on the pore size,specific surface area,mechanical properties and hydrophilicity of the nanofiber membranes were investigated.It was found that the tree-like structure significantly decreased the pore size and dramatically enhanced the specific surface area,mechanical properties and hydrophilicity of the membranes.The filtration performances of the common PVDF nanofiber membranes and the tree-like nanofiber membranes with different basis weight to 0.26?m NaCl particles were measured.The results showed that in comparison with common PVDF nanofiber membranes,the filtration efficiency of tree-like nanofiber membranes with the basis weight of 1 g m-2 was 99.999%and the pressure drop was only 124.2 Pa.The retention ratios of the nanofiber membranes with different tree-like structure contents to 0.3 ?m polystyrene(PS)particles were also tested.It was found that the PVDF tree-like nanofiber membrane with a thickness of 30±2 ?m showed a satisfactory retention ratio of 99.9%and a high pure water flux of 2.88×104 L m-2h-1 under the pressure of 0.1 MPa.From the cross-section images of the membranes after a filtration test could be found that the filtration was mainly dependent on surface retention,which was helpful for the backflush reuse.Based on the larger specific surface area of the tree-like nanofiber membrane,a novel MnO2@PVDF tree-like nanofiber membrane as a highly Pb2+ adsorbent was designed by in situ polymerization of pyrrole monomer,and subsequently reacted with KMnO4 solution to deposit MnO2.It was found that the MnO2 uniformly loading on the surface of the tree-like nanofiber and the hydrophilicity of the adsorbent enhanced after loading MnO2.The kinetics of Pb2+ adsorption was found to follow a pseudo-second-order rate model.The adsorption isotherms were fitted best with the Langmuir isotherm model.The thermodynamics analysis confirmed that the adsorption process was endothermic and spontaneous.The adsorbent also exhibited good selectivity and high recyclable removal efficiency.XPS analysis showed that ion exchange was the main mechanism for Pb2+ adsorption.Taking advantage of the dehydrofluorination of polyethylene polyamine(PEPA),a smart PVDF-g-PAA tree-like nanofiber membrane with pH-responsivity was fabricated through homogeneous solution polymerization and electrospinning process.The effects of PEPA contents and acrylic acid contents on the morphologies,mechanical properties and hydrophilicity of nanofiber membrane were investigated.The results showed that the C=C bonds was successfully formed after adding PEPA.When the PEPA content was less than 10%.the nanofiber membrane exhibited good tree-like morphology and the mechanical properties of the membranes decreased with the increase of the PEPA content.Thus the PEPA content was selected to be 5%.With the increasing of acrylic acid content,the tree-like nanofibers contents increased,the pore size reduced and the mechanical properties decreased.When the acrylic acid content was 10%,the nanofiber membrane exhibited good pH-responsive oil/water wettability.More importantly,the as-prepared membrane realized on-demand oil/water separation using gravity alone by switching the pH of the medium.Both separations exhibited excellent efficiency(>99%)and flux(9600 L/m2h).In this paper,the PVDF tree-like nanofiber could be controllably fabricated by one-step electrospinning.The PVDF tree-like nanofiber membrane possessed extremely small pore size and large specific surface area,which made it a promising material for air/liquid filtration,heavy metal ions adsorption and oil/water separation fields and opened a new way for the application of electrospinning nanofibers. |
PDF Full Text Request